I stayed in Lancaster for a year after college, then moved to New Mexico for about a year and a half. Then I moved to DC, and while I've been varying distances from the District itself I've basically been here ever since.
Agreed on the difficulty of making friends as you get older. What generates friendships is sharing common experiences. In high school and college you're placed into classes and living situations with random people and it's easy to do stuff together. Many of my best friends in DC were people I lived in group houses with. Others were from sports teams--soccer, softball. My best new friends of the past couple years are the guys from the band, which makes sense--we get together for practice almost weekly, play gigs, drink beer.
It doesn't quite translate to work, especially as you get older. When you're in your 20s and still going out a lot it can be easy to socialize with co-workers the same age if you're cool with that. But I know as I've gotten older, I've largely (though not entirely) kept work and personal life separated.